Recently, as an IT technology has been developed, medical imaging devices that non-invasively shows an interior of a body in an image form to provide information necessary to accurately diagnose diseases have been widely used. Among the above-mentioned medical imaging devices, examples of a tomography image obtainer include a computed tomography (CT), a magnetic resonance imaging (MRI), a nuclear medicine imaging device, and the like. Among these, the computed tomography (CT) and the magnetic resonance imaging (MRI) provide a detailed anatomical image of the body, and the nuclear medicine imaging device using a radioactive isotope provides an image showing a physiological phenomenon in the body.
Particularly, a positron emission tomography (PET) among the nuclear medicine imaging devices images an intra-body distribution of radioactive pharmaceuticals after injecting the radioactive pharmaceuticals emitting positron into the body which becomes a target of research and diagnosis through an intravenous injection or inhalation. The above-mentioned PET image is used as a tool that measures several physiopathological phenomena, and has an advantage capable of imaging concentration of neuroceptor and delivery, and gene as well as measuring biochemical phenomena such as a blood flow rate, a basal metabolic rate, and a synthesis rate.
In the positron emission tomography technology described above, spatial resolution and sensitivity are determined as the most important factors, wherein the spatial resolution means capability capable of spatially distinguishing radioactive sources which are adjacent to each other in the image obtained from the positron emission tomography. A decrease in the above-mentioned spatial resolution increases an image spread effect and causes a result that underestimates radioactive concentration of a small structure. Accordingly, examples of a method for improving spatial resolution include a use of scintillation crystal having a small size, a separate signal processing, improvement of an image reconstruction method, and the like.
In addition, sensitivity is an indicator indicating gamma rays detected by the PET among the gamma rays generated from the radioactive sources which are present within a field of view of a PET scanner. As main factors affecting on the above-mentioned sensitivity, there are a thickness of the scintillation crystal, a radius of a detector loop, and the like. In order to improve the above-mentioned sensitivity, a method using scintillation crystal having high stopping power and rapid decay time, a method for maximizing a solid angle coverage by reducing a size of a PET bore, a method for expanding an axial field of view, a method for minimizing dead time loss, etc., have been suggested.
Particularly, sensitivity in an axial direction of the PET system is highest at a center of an axis and is decreased toward an outer portion of the axis, and in this case, a problem occurs that a PET image obtained from the outer portion of the axis has decreased quality thereof.
In order to secure a field of view in the axial direction to solve the above-mentioned problem, a length of the axis is increased, and in this case, a problem occurs that overall costs of the system are increased.
A related art of the positron emission tomography detector and the positron emission tomography system using the same is as follows.
Related Art 1, which is Korean Patent No. 1088057 (registered on Nov. 23, 2011), relates to a detector module for a positron emission tomography (PET) and a positron emission tomography using the same. The detector module for a positron emission tomography according to Related Art 1 includes: a scintillation layer in which a plurality of rod type scintillators arranged to be in parallel to an axis direction of a detection ring are configured to be arranged in a pixel type of array and the pixel array in which the plurality of rod type scintillators are arranged is arranged so that a cross section of the detection ring in a radial direction forms a trapezoidal shape; a pair of light diffusing layers each connected to both ends of the scintillation layer to diffuse scintillation signals transferred from the respective scintillators configuring the scintillation layer; a pair of optical sensor arrays each connected to the pair of light diffusing layers to convert the scintillation signals transferred from the light diffusing layers into an electrical signal; and a pair of detection circuit unit each connected to the pair of optical sensor arrays to compare and analyze the electrical signals transferred from the optical sensor arrays through a preset detection algorithm and detect reaction positions of gamma rays within the scintillation layer, wherein the gamma rays emitted from a photographing region are incident through side portions of the plurality of rod type scintillators arranged to be in parallel to the axis direction of the detection ring.